Natural gas refers to gaseous hydrocarbons that are produced from a subterranean formation. Natural gas comprises predominately methane (CH4) with lesser amounts of ethane (C2H6), propane (C3H8), butane (C4H10), and perhaps a small amount of heavier hydrocarbons. Propane and heavier components (C3+) tend to be separated from the natural gas, liquefied, and often sold as fuel for various purposes. The remaining methane and ethane, which may be liquefied to facilitate transportation and storage (e.g. as liquefied natural gas (LNG)) is often sold into a pipeline system as commercial natural gas.
In the United States, there are limits on the thermal potential energy, often referred to as the heating value, of commercial natural gas. Typically, commercial natural gas that is sold into a pipeline system is limited to a heating value of about 1,100 British Thermal Units per standard cubic foot (BTU/scf). Methane has a heating value of about 1,000 BTU/scf, whereas ethane has a heating value of about 1,700 BTU/scf. As a result, commercial natural gas is typically deethanated to meet the pipeline heating value limits. The deethanization process produces a substantial amount of ethane, which has little commercial value. In fact, many high-ethane content natural gas wells are shut-in (e.g. the natural gas is kept in the subterranean formation) because the cost of purifying the natural gas to meet the pipeline heating value specifications exceeds the value of the product streams. Additionally, gas may be shut in at the well because ethane extraction is necessary for the gas to meet pipeline specification, but there is no market for the extracted ethane.